Cable companies have become the leading players in the search for ways to expand the ATM-based NII (National Information Infrastrcucture) backbone network into the homes. However, the community networks must support two-way asymmetric traffic patterns and arbitrate multiple accesses for available bandwidth.
HFC is gradually becoming the standard for many cable companies. In order to support interactive information service, the conventional one-way transmission HFC network has been incorporated with optical fibers to become a two-way transmission optical-fiber-HFC mixed network. Further details of accomplishing the interactive multimedia service includes:
1. Establishing an optical fiber for a long distance transmission between the headend and a cluster of homes (HFC is still used for a short distance transmission between the cluster of homes and the terminal units). PA1 2. Establishing upstream signal amplifiers on the network for the upstream channel between the headend and the terminal units. PA1 3. Establishing an upstream MAC (Multiple Access Control) protocol in the controller of the headend. PA1 4. Introducing an interactive multimedia service into the server of the headend, which is accessible to the terminal units. PA1 5. Connecting the optical-fiber-HFC mixed network with the ATM-based NII backbone network. PA1 a) updating on-line stations in said plurality of stations, and optionally balancing loads in all the upstream channels; PA1 b) positioning said on-line stations according to transmission delays between said on-line stations and said headend and in an ascending order; and PA1 c) scheduling a transmission starting time and a transmission duration for each station of said on-line stations, which comprises calculations based on number of requested transmission cells and priority levels of the requested transmission cells provided by each of said on-line station to said headend at the end of its preceding transmission duration, and said transmission delay. PA1 t.sub.i is the transmission duration for the i.sup.th on-line station; PA1 b.sub.i is a requested number of best-effort transmission cells of the i.sup.th on-line station; PA1 G.sub.i is a requested number of guaranteed transmission cells of the i.sup.th on-line station; PA1 g.sub.i a minimum number of guaranteed transmission cells of the i.sup.th on-line station; PA1 .alpha..sub.i is urgency of guaranteed transmission cells of the i.sup.th on-line station; PA1 .beta..sub.i is urgency of best-effort transmission cells of the i.sup.th on-line station; PA1 CBT is the number of slots within a transmission cycle; and PA1 W.sub.i is a guard-band time overhead of the i.sup.th on-line station. PA1 i is defined as above; PA1 j is an integer of 1 to i-1; PA1 Si is the transmission starting time of the i.sup.th on-line station; PA1 t.sub.j is the transmission duration for the j.sup.th on-line station; and PA1 .tau..sub.i is the transmission delay of the i.sup.th on-line station.
The present invention is directed to an efficient upstream MAC (Multiple Access Control) protocol mentioned in the above item 3), which is also a goal to be achieved by IEEE 802.14 Cable TV LAN MAC/PHY committee. The conventional LAN protocols, for example CSMA/CD and R-ALOHA protocols, are not suitable for use in the case, because the optical-fiber-HFC mixed network has only the upstream and downstream channels. In optical-fiber-HFC mixed network the subscribers in the feeder cable can only listen to the downstream from the headend and transmit in the allocated upstream, and the headend, on the contrary, can only listen to the upstream from the subscribers and transmit in the downstream channel. The subscribers can not listen directly to the upstream transmissions from other subscribers, and hence they are incapable of coordinating their transmissions all by themselves. Moreover, many subscribers compete with one another in the upstream channel, so that the collision ratio under heavy traffic is high and thus inefficient.
Many MAC protocols have been proposed and studied. They can be classified into two categories: distributed protocols and centralized protocols. There is no central controller in the distributed protocols. The centralized protocols provide better timing mechanisms in avoiding collisions. This kind of protocols, proposed by many organizations, include MLAP(MAC Level Access Protocol) of IBM Corp. [Chatschik Bisdikian, Bill McNeil, Rob Norman and Ray Zeisz, "MLAP: A MAC Level Access Protocol for the HFC 802.14 Network", IEEE Communication Magazine, pp. 114-121, March 1996.], XDQRAP(Extended Distributed Queuing Random Access Protocol) of Scientific-Atlanta, Inc. [Frank Koperda, Bouchung Lin, "First Phase Simulation for XDQRAP", IEEE 802.14-96/062, draft proposal.], ADAPt (Adaptive Digital Access Protocol) of AT&T Bell Lab. [James E. Dail, Miguel A. Dajer, Chia-Chang Li, Peter D. Magill, Curtis A. Siller, Jr., Kotikalapudi Sriram, and Norman A. Whitaker, "Adaptive Digital Access Protocol: A MAC Protocol for Multiservice Broadband Access Networks", IEEE Communication Magazine, pp. 104-113, March 1996.], UniLINK protocol of LANcity corp. [John M. Ulm, LANcity Corp. "A MAC proposal for 802.14", IEEE 802.14/95-134, draft proposal.], FPP(Framed Pipeline Polling) protocol of NEC corp. [Morihisa momona, Shuntaro yamazaki, "Framed Pipeline Polling for Cable TV Networks", March 1995, IEEE 802.14-96/076, draft proposal.], CPR (Centralized Priority Reservation) protocol of Georgia Institute of Technology [Dolors Sala, John O. Limb, "A Protocol for Efficient Transfer of Data over Fiber/Cable Systems", pp. 904-911, IEEE INFOCOM'96.], and traditional TDMA (Time Division Multiple Access), etc.
In the centralized protocols proposed above, a fixed division approach is commonly utilized. The fixed division approach is more or less not compatible to a sudden change of information transmission, and thus can not reach the best throughput and utilization.
A main object of this invention is to provide an improved method of upstream multiple access control in a transmission system, and in particular in a optical-fiber-HFC mixed communication network, which has advantages of high efficiency and pipelined transmission.